A flat panel display (FPD) such as an organic EL (electro-luminescence) display (OELD), or a plasma display panel (PDP) has such a structure that a glass substrate for an element having a light-emitting element formed and a glass substrate for sealing are disposed to face each other and the light-emitting element is sealed in a glass package comprising two such glass substrates bonded (Patent Document 1). A liquid crystal display device (LCD) also has such a structure that a liquid crystal is sealed between two glass substrates. Further, for a solar cell such as a dye-sensitized solar cell, application of a glass package having a solar cell element (photoelectric conversion element) sealed with two glass substrates has been studied (Patent Document 2).
As a sealing material to seal the space between two glass substrates, application of a sealing glass excellent in the moisture resistance, etc. is in progress. Since the sealing temperature of the sealing glass is at a level of from 400 to 600° C., properties of an electronic element portion of the OEL element or the like will be deteriorated when firing is conducted by using a conventional heating furnace. Accordingly, it has been attempted that a sealing material layer containing a sealing glass (glass frit) and a laser absorbent is disposed between sealing regions provided on the peripheral portions of two glass substrates, and the sealing material layer is irradiated with a laser light to heat and melt the sealing material layer to conduct sealing (Patent Documents 1 and 2).
In a case where laser sealing is applied, first, a sealing material is mixed with a vehicle to prepare a sealing material paste, which is applied to a sealing region of one glass substrate and heated to the firing temperature (a temperature of at least the softening temperature of the sealing glass) of the sealing material to melt the sealing glass and burn it on the glass substrate to form a sealing material layer. Further, in the procedure of heating the sealing material to the firing temperature, the organic binder is burnt out by thermal decomposition. Then, the glass substrate having the sealing material layer and the other glass substrate are laminated by means of the sealing material layer, and the laminate is irradiated with a laser light from the side of one of the glass substrates to heat and melt the sealing material layer thereby to seal an electronic element portion provided between the glass substrates.
To form the sealing material layer, a heating furnace is commonly used. Patent Document 3 discloses to conduct a first heating procedure of removing the organic binder in a step of forming the sealing material layer and a second heating procedure of burning the sealing material. In the first heating procedure, a glass substrate is heated from its rear side by means of a hot plate, an infrared heater, a heating lamp, a laser light or the like. In the second heating procedure, in the same manner as a conventional firing step, the entire glass substrate is heated by means of a heater in a heating furnace. In the process disclosed in Patent Document 3 also, burning of the sealing material is carried out by heating the entire glass substrate by means of a heating furnace.
By the way, for a glass package for FPD, an organic resin film such as a color filter is formed not only on a glass substrate for an element but also on a glass substrate for sealing. In such a case, if the entire substrate is heated in a heating furnace, the organic resin film will be damaged by heat, and accordingly a firing step by a common heating furnace cannot be applied even at the formation of the sealing material layer on the glass substrate for sealing. Further, in a dye-sensitized solar cell, an element film or the like is formed even on the facing substrate side, it is required to suppress thermal deterioration of the element film or the like in the firing step. Further, since the firing step by a heating furnace usually requires a long time and consumes a lot of energy, improvement is required from the viewpoint of the reduction in the production steps and the production cost and the energy saving also.
Patent Document 4 discloses application of a sealing material comprising a paste prepared by mixing low temperature melting glass (sealing glass), a binder and a solvent to one of panel substrates, followed by laser annealing the sealing material. However, the sealing glass may not uniformly be melted merely by laser annealing the sealing material. That is, only the vicinity of the surface of the coating layer of the sealing material may be melted, and melting of the sealing glass of the entire coating layer may be inhibited. If only the vicinity of the surface of the coating layer of the sealing material is melted and vitrified, emission of a gas formed by thermal decomposition of the binder to the outside will be deteriorated, thus leading to defects such as internal air bubbles and surface deformation of the sealing material layer. Such defects of the sealing material layer may deteriorate the air tightness of the panel and the bond strength.
Prior Art Documents
Patent Documents
Patent Document 1: JP-A-2006-524419
Patent Document 2: JP-A-2008-115057
Patent Document 3: JP-A-2003-068199
Patent Document 4: JP-A-2002-366050